Problematical fossil cnidarians from the Upper Ordovician of the north-central USA

28 Pages·1996·12.9 MB·English

by  Heyo Van Iten

PROBLEMATICAL FOSSIL CNIDARIANS
FROM THE UPPER ORDOVICIAN OF
THE NORTH-CENTRAL USA
by HEYO VAN ITEN, JULIE ANN EITZKE and ROBT S. COX
Abstract. Sphenothallus sp. and eight species of conulariids, distributed among the genera CUmacocomis,
Comilaria, Glyptocomdaria and Metaconularia, occur in the Elgin Member of the Maquoketa Formation
(upper Ordovician) ofnorth-eastern Iowa and south-eastern Minnesota, USA. Seven ofthe eight conulariid
species exhibit internal test structures at their corners and/or midlines. Comparisons ofthese test structures
withinternalthecalstructuresofcoronatidscyphozoanscorroboratethehypothesisthatconulariidsweremore
closely related to scyphozoan cnidarians than they were to any other extant taxon of comparable rank.
Sphenothallus and conulariids occur in all four Elgin Member biofacies. However, the distribution of
Climacoconus and Conularia is facies-dependent, with Climacoconus occurring predominantly in the
brachiopod-echinoderm biofacies and the basal Maquoketa phosphorite, Conularia splendida predominantly
in the trilobite-dominated biofacies, and C. trentonensispredominantly in the brachiopod-echinoderm, mixed
faunas and graptolite shales biofacies. Conulariids commonly occur in monospecific clusters, possibly clonal
inorigin,andsomespecimensshoworientationalevidenceoforiginalattachmentto Sphenothallusornautiloid
shell material. Together with previously reported data on the distribution and biostratinomy ofSphenothallus
and conulariids, these results suggest that both taxa were sessile benthic organisms that inhabited all major
Elgin Member bottom environments, including a shallow, oxic carbonate shelf and a deeper, dysoxic shelf
margin and shale basin slope. One new species, Climacoconus sinclairi, is described.
Conulariids and their possible close relative Sphenothallus Hall, 1847 are widely distributed in
Palaeozoic marine strata and are often mutually associated. Both may occur in exceptional
abundance in certain rock units. Among the best known units previously discussed are the middle
Ordovician Sarka and Dobrotiva formations of Bohemia (conulariids; e.g. Havlicek 1966), the
upper Ordovician May Sandstone of Brittany (conulariids; e.g. Boucek 1928) and the upper
Ordovician Collingwood Formation of Ontario and Quebec (conulariids and Sphenothallus; e.g.
Bolton 1994). Sphenothallusandconulariidsoften occurindarkshalesand limemudstonesin which
normal marine taxa such as echinoderms and articulate brachiopods are rare or absent. Together
with evidence suggesting that Sphenothallus and conulariids were sessile benthic organisms (e.g.
Bodenbenderetal. 1989; Van Iten 19916), such occurrences raisethepossibility that these taxa were
capable of living in bottom waters subject to oxygen depletion and/or other forms of stress.
Recent analyses oflarge numbers ofSphenothallus and conulariid specimens from deposits such
as those mentioned above have substantially increased our knowledge of anatomical variation
within these organisms, and have provided evidence bearing on alternative interpretations oftheir
mode oflife and life history (e.g. Bodenbender et al. 1989; Van Iten 1991c, 1992a; Van Iten et al.
1992; Jerre 1993, 1994). This work has also contributed to discussions ofthe phylogenetic affinities
ofthese taxa, one or both ofwhich have been variously interpreted as annelids or other ‘worms’
(Sphenothallus and conulariids; e.g. Clarke 1913; Moore et al. 1952; Mason and Yochelson 1985;
Fauchald et al. 1986; Babcock 1991), hemichordates or chordates (conulariids; Termier and
Termier 1949, 1953; Steul 1984), an independent phylum (conulariids; e.g. Kozlowski 1968;
Babcock and Feldmann 1986a; Babcock 1990, 1991; Yochelson 1991) or close relatives of
hydrozoan or scyphozoan cnidarians (Sphenothallus and conulariids; e.g. Price 1920; Kiderlen
IPalaeontology,Vol. 39, Part4, 1996, pp. 1037-1064,3pls| © The Palaeontological Association
/
PALAEONTOLOGY, VOLUME
1038 39
1937; Moore and Harrington 1956; Chapman 1966; Werner 1966, 1967; Glaessner 1971, 1984;
Bischoff 1978; Grasshoff 1984; Van Iten 1991o, 1992a, \992b, 1992c; Van Iten and Cox 1992; Van
Iten et al. 1992; Jerre 1994).
The present paper addresses the taxonomy and palaeoecology ofSphenothallus and conulariids
in the Elgin Member ofthe Maquoketa Formation (upper Ordovician) ofnorth-eastern Iowa and
south-eastern Minnesota, USA. The purpose ofthis study is to document the exceptionally diverse
Elgin Sphenothallus/comxldLx'nd fauna and to interpret aspects of the anatomy and distribution of
these taxa having an important bearing on discussions of their affinities and palaeoecology. The
Maysvillian (late Caradoc) Elgin Member has long been known for its abundant trilobites,
echinoderms, brachiopods and molluscs(e.g. Slocum 1914; Slocumand Foerste 1920; Walter 1924;
Ladd 1929; MillerandYoungquist 1949; Tasch 1955; Bretsky and Bermingham 1970; Whittington
1971). Until now, however, this unit had not been recognized as a major Sphenothallus conu\2iv'\\d
horizon. The Elgin Member contains eight species of conulariids representing the genera
Climacoconus Sinclair, Comilaria Miller in Sowerby, Glyptoconularia Sinclair and Metaconularia
Foerste. One species is new. With the possible exceptions ofthe middle Ordovician Trenton Group
ofNew York and Quebec and the lower Silurian Manitoulin Dolomite ofnorthern Michigan and
south-western Ontario (Sinclair 1948), no other North American stratigraphical unit contains as
many conulariid genera and species as does the Elgin Member.
The Elgin Member consists of intertonguing shales and carbonates deposited in a density-
stratified epeiric sea the bottom waters ofwhich were dysoxic or anoxic over large areas (Witzke
1980, 1987; Witzke and Kolata 1989). Coupled with the unusually high diversity and abundance of
Elgin Sphenothallus and conulariids, the substantial facies variation of this unit makes it an
attractivesettingfortheanalysis ofthepalaeoecologyofthesetwogroups. Inparticular,conulariids
have been variously interpreted as sessile benthic (e.g. Babcock etal. 1987a, \9%lb\ Van Iten 1991a,
19916), nektonic (e.g. Havhcek 1966) or planktonic or pseudoplanktonic organisms (e.g.
Ruedemann 1934; Babcock and Feldmann 1984, 19866). As will be discussed below, conulariids
occur in all Elgin facies, but the distribution ofconulariid species is facies-dependent. Moreover,
conulariid specimens may occur in undisturbed life clusters or preserve orientational evidence of
primary apical attachment to nautiloid shells and Sphenothallus tubules.
MATERIALS AND METHODS
The present study is based on direct examination ofspecimens collected from over 20 localities in
the northern and central parts of the Maquoketa outcrop belt of north-eastern Iowa and south-
easternMinnesota(Text-fig. 1 ; Appendix 1). Thesamplemcomnsistsofapproximately350macroscopic
specimens, mostlyconulariids, and minute (about 1 to 2 long) conulariidand Sphenothallustest
fragments (e.g. PI. 2, fig. 2) obtained by dissolving pieces oflimestone approximately 1 kg in mass
in 4N formic acid. Test fragments were picked from undissolved residues washed on a 63 pm brass
screen. The limestone samples (Appendix 2) were collected in place, at 1 m intervals, from localities
(4, 8, 16-17 and 19) that together expose most of the currently recognized stratigraphical units
within the carbonate portion ofthe member. Test fragment samples are housed in the Department
of Geology, State University of Iowa, under collection number 84492.
AbbreviationsofNorthAmericaninstitutionshousingspecimensexaminedinthisstudyareasfollows:AC,
AugustanaCollege, RockIsland, Illinois;AMNH,AmericanMuseumofNaturalHistory,NewYork; CCPC,
DepartmentofGeology,CarletonCollege,Northfield,Minnesota; FMNH, Field MuseumofNaturalHistory,
Chicago; GSC, Geological SurveyofCanada, Ottawa; NYSM, NewYorkStateMuseum,Albany; SUI, State
University of Iowa, Iowa City; UMMP, University of Michigan Museum of Paleontology, Ann Arbor;
UMPC, University of Minnesota Paleontology Collections, Minneapolis; WSU, Winona State University,
Winona, Minnesota.
VAN ITEN £T/1L.: PROBLEMATICAL ORDOVICIAN CNIDARIANS 1039
I I
TEXT-FIG. 1. Map of the Maquoketa Formation/Elgin Member (upper Ordovician) outcrop belt in north-
eastern Iowa and south-eastern Minnesota, USA. Numbered dots represent collecting localities that yielded
Sphenothallus and/or conulariid specimens examined in the present study (see Appendix 1).
STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS
Maquoketa Formation
The Maquoketa Formation (considered to be a group by stratigraphers in Illinois, Indiana and
Wisconsin; e.g. Gray 1972; Sivon 1980; Kolata and Graese 1983) ranges from Maysvillian to
Richmondian (Caradoc to Ashgill) and underlies much of the north-central United States east of
1040 PALAEONTOLOGY, VOLUME 39
the Transcontinental Arch (Witzke 1980, 1987; Witzke and Kolata 1989). The formation consists
oftwo majorfacies chertyshelfcarbonates, preservedmainlyinthesubsurfaceandextendingfrom
:
eastern Iowa to the Transcontinental Arch; and shale-dominated strata developed east and south
ofthis region, primarily in south-eastern Wisconsin, Illinois, Indiana, north-eastern Missouri and
eastern Iowa. Shale-dominated strata occur at the surface primarily in south-eastern Wisconsin,
western Illinois, north-eastern Missouri, south-eastern Minnesota and north-eastern Iowa. In
north-eastern Iowa and south-eastern Minnesota, these beds range from about 30 to 100 m thick
andcropoutsporadicallyin anarrow, north-west-south-east-trendingbeltthatextendsfromnorth-
eastern Clinton County, Iowa to southern Fillmore County, Minnesota (Parker et al. 1959; Parker
1971 Text-fig. 1). In most ofthe north-western halfofthe outcrop belt the Maquoketa Formation
;
consists of five members. Listed in ascending order, these are the Elgin Shaly Limestone, the
Clermont Shale, the Fort Atkinson Limestone, the Brainard Shale and the Neda Shale. Duein part
to pre-mid Devonian erosion, only the Elgin Member is present in Minnesota. South of a line
extending through southernmost Clayton and Fayette counties, Iowa, the Elgin Member consists
mainly of dark shales, and the rest of the Maquoketa Formation is composed almost entirely of
lighter-coloured shales assigned to the Brainard Member. In both north-eastern Iowa and south-
eastern Minnesota, the Maquoketa (Elgin Member) rests conformably on shaly limestones ofthe
upper Ordovician Dubuque Formation, while the top of the formation is marked by an
unconformity overlain by lower Silurian dolostones (north-eastern Iowa) or middle Devonian
limestones (south-eastern Minnesota).
Elgin Member
The Elgin Member in the lowa/Minnesota outcrop belt represents a shallowing-upward sequence
showing maximum facies variation along a north-west-south-east transect (Witzke 1980, 1987;
Text-fig. 2). Except in Minnesota, where Maquoketa strata have been deeply eroded, the Elgin
Member is conformably overlain by shales of the Clermont or Brainard members. In the
lowa/Minnesota border area, in southernmost Fillmore County, Minnesota and the northernmost
partsofHowardandWinneshiekCounties, Iowa, theElginconsistspredominantlyofgreyandlight
grey biomicrites and has been subdivided into four subunits, designated Lithosomes I-IV (Bayer
1967; Elias et al. 1988; Text-fig. 2). Lithosome I is characterized by a sparse, low diversity
macrofauna dominated by graptolites and the trilobite Isotelus iowensis Owen. Lithosomes II and
III are cherty and contain abundant, diverse invertebrate faunas including articulate brachiopods,
pelecypods, nautiloids, trilobites, crinoids, sponges and solitary rugose corals.
South of the lowa/Minnesota border area, in a region encompassing parts of south-eastern
Winneshiek, south-western Allamakee, north-eastern Fayette and north-western Clayton counties,
Iowa, the Elgin Member consists predominantly of thin biomicrites interbedded with brown
graptolitic shales. Elgin Member strata can be subdivided over much of this area into five units,
designated Units 1-5 (Parker et al. 1959; Text-fig. 2). Unit 1 is separated from the underlying
Dubuque Formation by a thin phosphate horizon, the basal Maquoketa phosphorite, that occurs
at the base of the Elgin Member throughout most of north-eastern Iowa. Units 1-3 are similar
palaeontologically to Lithosome I, while Units 4 and 5 contain diverse macrofaunas consisting of
abundant trilobites as well as articulate brachiopods, nautiloids, gastropods, crinoids, cystoids and
sponges.
In the southern part ofthe Maquoketa outcrop belt, in south-eastern Fayette, southern Clayton
and eastern Dubuque, Jackson and Clinton counties, Iowa, the Elgin Member consists mostly of
brown to grey or black, graptolitic shales with locally abundant inarticulate brachiopods {Lingula)
and rare trilobites (Text-fig. 2). In the vicinity of the village of Graf, north-eastern Dubuque
County, the upper part of the unit exhibits numerous thin interbeds of dolostone containing
abundant nautiloids and rare crinoids and bryozoans.
The lithological units described above together define four mutually intertonguing biofacies
(Witzke 1980, 1987; Text-fig. 2). Moving from north-west to south-east, these are (1) the
brachiopod-echinoderm biofacies (Lithosomes II and III ofBayer 1967; Units 4 and 5 ofParker et
VAN ITEN ET AL.: PROBLEMATICAL ORDOVICIAN CNIDARIANS 1041
lithologies: biofacies: 50km
carbonates m0^ brachiopod-echinoderm
[ I
interbeddedcarbonates
andbrownshales trilobite-dominated
nn
browntoblackshale mixedfaunas
P phosphorite [G] graptoliteshales
A chert
TEXT-FIG. 2. North-west-south-east stratigraphical cross section of the Elgin Member of the Maquoketa
Formation (upper Ordovician) in north-eastern Iowa and south-eastern Minnesota, USA. Stratigraphical
column labelled ‘FC’ represents the Fitzgerald Creek measured section of Parker et al. (1959, fig. 2b);
stratigraphicalcolumn labelled ‘18’ (Focality 18) represents themeasured sectionofBayer(1967, fig. 2). Text-
figure modified from Witzke (1987, fig. 4).
al. 1959); (2) the trilobite-dominated biofacies (Lithosome I ofBayer 1967; Units 1-3 ofParker et
al. 1959); (3) the mixed faunas biofacies (alternating brown to black graptolitic shales and
phosphatic dolomites); and (4) the graptolite shales biofacies (brown to black graptolitic shales
stratigraphically below and lateral to the mixed faunas beds). These four biofacies were originally
deposited in ‘contrasting water masses ofa stratified epicontinental seaway’ (Witzke 1987, p. 239),
in ‘three general bathymetric settings: (1) shallow carbonate shelf [brachiopod-echinoderm
biofacies]; (2) shelf margin (deepening to the southeast) [trilobite-dominated and mixed faunas
biofacies] and (3) basin slope [graptolite shales biofacies]’ (Witzke 1987, p. 237). The shallow
;
carbonate shelf, represented by Lithosomes II and III and Units 4 and 5, was deposited in areas
whereawell-mixed, oxicupperwatermass impinged onthe sea floor. Depositionherewasgenerally
belowfair-weatherwavebasebut abovestormwavebase(Eliasetal. 1988). Onmoreproximal parts
of the shallow carbonate shelf, sandy lime muds lacking benthic organisms (Lithosome IV) were
deposited in waters that were highly restricted. Below the oxic upper water mass, in the proximal
shelf slope environment, asaphid-graptolite mudstones of the trilobite-dominated biofacies were
deposited in the upper part of a zone of increasing density and decreasing oxygen content, or
pycnocline. Deposition ofthe grey to dark grey, pyriticasaphid-graptolitemudstones ofUnit 1 and
Lithosome I probably occurred in dysoxie waters. The distal shelfslope, largely deposited in lower
pycnoclinal waters that were further depleted in oxygen, was the site of graptolitic shale
sedimentation (lowermost mixed faunas facies and brown to grey organic shales of the graptolite
shales biofacies). Below the pycnocline, deposition of grey to black laminated shales eommonly
lacking benthic invertebrates (parts of the graptolite shales biofacies) took place at the base of a
relatively deep water mass that was dysoxie to anoxic.
;
PALAEONTOLOGY, VOLUME
1042 39
Based on these interpretations of depositional environments and on inspection of exposures
showing transitions between facies, we propose the following chronostratigraphical correlations of
Elgin Membersubunits. As suggestedbyWitzke(1980), thebasal Maquoketaphosphoritein north-
eastern Iowa probably represents a condensed interval that correlates with Lithosome I and
laterally equivalent parts of Lithosome II in south-eastern Minnesota. Units 1-3 of the trilobite-
dominated biofacies can be correlated with Lithosome III and the upper part ofLithosome II (see
for example Bayer’s (1967) measured section for Locality 18 (Bayer Locality L-231)) and with the
lowerpart ofthe graptolite shales biofacies (includingunits 1-3 ofWitzkeand Glenister’s(1987, fig.
3) Graf, Iowa section). Linally, Units 4 and 5 probably correlate with Lithosomes III and IV and
with the mixed faunas and upper graptolite shales biofacies (in southern Clayton County, Unit 4
may pass southward into strata assignable to Unit 3).
ANATOMICAL TERMINOLOGY
Use ofanatomical terminology in this paper is generally consistent with precedents to be found in
Sinclair (1940, 1942, 1952), Moore and Harrington (1956) and Van Iten (1992a). Two new terms,
both pertaining to test features of Conularia, are introduced here. As indicated by inspection of
sectioned and broken material, the interspaces (the regions between thecrests ofthe transverse ribs)
ofmost currently recognized species ofConulariaare longitudinallycorrugated (PI. 3, hgs 1, 3). The
crests ofthecorrugations (as seen viewingthe test’sexteriorsurface) will bereferred to as interspace
ridges, while the troughs between the crests will be referred to as interspace furrows.
SYSTEMATIC PALAEONTOEOGY
Phylum CNIDARIA Hatschek, 1888
Class, Order, Lamily Uncertain
Genus sphenothallus Hall, 1847
SpJienothallus sp.
Plate 1, figure 8; Plate 2, figure 1
Material. SUl 84486, 84493b, 84495i-k, 84496, 84497a, 84498, 84499a, 84500, 84514e-f, 84517b (>50
specimens).
EXPLANATION OF PLATE
1
Figs 1, 6. ConulariasplendidaBillings, 1866; upperOrdovician,MaquoketaFormation,ElginMember, Unit 1
near the mouth ofOtter Creek in Elgin, Fayette County, Iowa, USA. 1, SUI 49979a; external view oftwo
faces of a flattened but more or less complete specimen; x L7. 6, SUI 49979; radial cluster of eight
specimens, all of which are oriented parallel to bedding and occur in a grey, pyritic lime mudstone with
graptolites and asaphid trilobite fragments; xO-66.
Fig. 2. Conularia trentonensis Hall, 1847; SUI 61508; upper Ordovician, Maquoketa Formation. Elgin
Member, ?Unit 3; north-eastern Iowa (Eocality 16), USA; external view of two faces of a flattened
specimen; x 1-6.
Fig. 3. Conularial sp.; SUI 84491; upper Ordovician, Maquoketa Formation, Elgin Member, Lithosome II;
south-eastern Minnesota (Locality 18), USA; internal mould ofa partial face and two corners; x2.
Figs 4, 8. Climacoconus quadratus (Walcott, 1879); upper Ordovician, Maquoketa Formation, Elgin
Member,LithosomeI;south-easternMinnesota, USA.4, SUI84494;Locality 18;externalviewoftwofaces
andacorner; x2-6. 8,SUI 84493a;Locality 19;partialexternalmouldsoftwospecimensorientedwiththeir
apex next to a tubule ofSphenothallus sp. (SUI 84493b); x4-3.
Fig. 5. Glyptoconularia gracilis (Hall, 1847); SUI 55065; upper Ordovician, Maquoketa Formation, Elgin
Member, mixed faunas biofacies; north-eastern Iowa (Eocality 2), USA; external mould ofpart ofa face
and two corners; x4-7.
Fig. 7. Climacoconussinclairisp. nov.; GSC94784;upperOrdovician, Maquoketa Formation, ElginMember,
Unit 3; north-eastern Iowa (Locality 11), USA; external view ofthe holotype; x 31.
PLATE
1
VAN ITEN et al., Conularia, Climacoconus, Glyptoconiilaria
1044 PALAEONTOLOGY, VOLUME 39
Horizon andlocalities. Elgin Member, Lithesome II (Localities 17b and 19), mixed faunas biofacies (Locality
2; bed 8 ofWitzke and Glenister (1987, fig. 3)), graptolite shales biofacies (Locality 1).
mm
Description. Partial tubules up to 90 long; tubules apatitic, finely lamellar, preserving one or both
longitudinal thickenings and, in some cases, small portions ofthe thin wall between the thickenings; tubules
gently tapered and strongly curved near the apical end; holdfasts not preserved.
Remarks. Sphenothallus is widely distributed in middle and upper Ordovician strata of North
America, where it is represented by at least two species, S. angustifolius Hall (the type species) and
S. splendens (Hall) (Bolton 1994). The Elgin Member specimens, while similar to these two species
in size and gross anatomy, are not sufficiently complete to allow detailed comparisons ofthe thin
testwallbetweenthe longitudinalthickenings. Asindicated bypreviousdiscussionsofSphenothallus
morphology (e.g. Mason and Yochelson 1985; Van Iten el al. 1992; Bolton 1994), this relatively
delicatepart ofthetubuleshowsinterspecificvariationin thedevelopment ofsurfaceornament. For
these reasons, the Elgin Member specimens are here left unassigned at the species level.
It is interesting to note that none ofthe Elgin Member Sphenothallus specimens examined in this
study preserves the holdfast. Abundant Sphenothallus with holdfasts have been found in mudrocks
at several other localities, including the Lower Carboniferous Calciferous Sandstone of Scotland
(Slater 1907) and Bear Gulch Limestone ofcentral Montana (Van Iten et al. 1992). Some of the
specimens from the Calciferous Sandstone are attached to conulariids (Paraconularia tenuis
(Slater)), while those from the Bear Gulch Limestone commonly are attached to ammonoid shells.
In addition to these specimens, abundant non-mineralized holdfasts, similar in gross anatomy and
microstructure to mineralized Sphenothallusholdfasts, and interpreted by Bodenbenderetal. (1989)
asSphenothallusremains, havebeen foundattachedtohardground surfacesin theupperOrdovician
Dillsboro Formation of Ohio.
Genus climacoconus Sinclair, 1942
Climacoconus sinclairi sp. nov.
Plate 1, figure 7; Plate 2, figure 4; Text-figure 3a
1992u Climacoconus sp. Van Iten, p. 341, text-fig. 3g.
Derivationofname. InhonourofthelateGeorgeWinstonSinclair,aleadingstudentofconulariidsand author
ofthe genus Climacoconus.
Types. Holotype, GSC 94784; paratypes, SUI 61531, 84487; Elgin Member, Units 3 (Localities 5, 11 and 14)
and 5 (Locality 10).
Diagnosis. Midlines straddled internally by a pair ofclosely spaced, adaperturally diverging files of
low, discrete, I-shaped ridges that each extend across an interspace.
Description. Three partial specimens, all broken well above theapex. Corners ofa given facediverge at about
14°; cornergrooves thickened, carinate;cornercarina low, keel-like, darkerincolourthantherest ofthetest;
exterior surface of the corner grooves crossed by extremely fine, closely spaced, adaperturally arching
transverse wrinkles that number about 25 per mm. Transverse ribs usually alternate at the midlines, straight
mm
within about 15 of the apex, elsewhere gently curved; transverse ribs increase in size and spacing
adaperturally, numbering 6 per 2mm about 15 mm above the apex and 4 per 2 mm about 25 mm above the
apex; transverse ribs offsetanddeflected toward theapertureon themarginsofthecornergrooves; within the
corner grooves the transverse ribs occur as low, broadly rounded, adaperturally arching ridges that extend
approximately two-thirds ofthe way across the grooves and alternate with ridges projecting from the other
side. Midline ridge zigzagged where the transverse ribs alternate, straight where the transverse ribs meet in
VAN ITEN ET AL.-. PROBLEMATICAL ORDOVICIAN CNIDARIANS 1045
opposition; midlines straddled along most oftheir length by a pair ofclosely spaced, adaperturally diverging
files oflow, discrete, I-shaped internal ridges, with each ridge extending across an interspace.
Comparisons. Climacocomis sinclairi differs from all previously published species of the genus
(Sinclair 1942, 1946; Hergarten 1985) in having a pair of seriated internal carinae at the midlines.
C. sinclairi further differs from C. bottnicus (Holm), C. scoticus (Lamont) and C. iirbanis Sinclair
inexhibitingalternationoftransverseribsat themidlines, and from C. batteryensis(Twenhofel) and
C. bureaui Sinclair in having carinate corners. The new species further differs from C. quadratus
(Walcott) in having the transverse ribs straighter.
Remarks. TheholotypeofC. sinclairiwasdescribedinanunpublishedPh.D. dissertation by Sinclair
(1948), who named it C. clermontanus (after the village ofClermont, Fayette County, Iowa). The
paired files ofI-shaped midline ridges are difficult to see in this specimen (the bases ofabout 15 of
the ridges have been exposed through exfoliation), and Sinclair (1948) did not mention them.
ABC
TEXT-FIG. 3. Camera liicidadrawingsoftransversecrosssectionsthrough Elginconulariidshavinginternal test
structuresattheircorners(C)andmidlines(M). a, Climacocomissinclairisp. nov. SUI61531 B, Climacocomis
; .
quadratus (Walcott); SUI 84501. c, Conularial sp.; SUI 84490. Scale bars represent 2-5 mm.
The threecurrently available specimens ofC. sinclairiwerecollected from Unit 3. Two additional
specimens, nowmissing, werecollectedbytheseniorauthorfromdolostonesnearthebaseofUnit 5.
Climacocomis with paired seriated carinae at the midlines also occur in the middle Ordovician
Platteville and Decorah formations near Minneapolis, Minnesota (Van Iten 1992n). Reposited
specimens are housed in collections of the Geological Survey of Canada (GSC 94785-94786;
approximately ten specimens) and the University of Michigan Museum of Paleontology (UMMP
2065; two specimens). Sinclair (1948) assigned the GSC specimens to C. concinmis (GSC 94785) or
C. mollis (GSC 94686), two species erected by Sinclair (1948) but never published. These specimens
UMMP
and 2065 may represent C. sinclairi, but it will be necessary to examine more complete
material before making a definitive identification.
Climacoconus quadratus (Walcott, 1879)
Plate 1, figures 4, 8; Plate 2, figure 2; Text-figure 3b
1879 Comilaria quadrata Walcott, p. 93.
1942 Climacocomis quadratus (Walcott); Sinclair, p. 226, pi. 3, figs 1-5.
1046 PALAEONTOLOGY, VOLUME 39
Material. SUI 62669, 81517-81518, 84492, 84493a, 84494, 84495a-h, 84501-84513, 84514a-d, 84515a-c (84
specimens); WSU unnumbered (six specimens).
Horizon and localities. Elgin Member, Lithosomes I and II (Localities 17b, 18 and 19), Units 1, 4 and 5
(Localities 7 and 9).
Description. Original length ofthe largest specimen exceeded 80mm. Faces equal in width or with one set of
opposingfaces uptoabout 1-5 timesaswideastheothertwo. Cornersofagivenfacedivergeatabout 12-15°;
corner grooves thickened, carinate; corner carina low, keel-like. Midlines also carinate; midline carina
extremely low. Transverse ribs generally alternate at themidlines; transverse ribs in the apical region straight,
rounded, meeting at the midlines at about 140°; elsewhere the transverse ribs have sharp crests, are gently
curved and intersect themidlines at about 90°; transverseribs increasein size and spacingadaperturally, with
mm mm mm
12per neartheapexand 1 or2per approximately80 abovetheapex;transverseribsslightlyoffset
on the margins ofthecornergrooves, deflected toward the aperture withinthegrooves and occurringthere as
low, broadlyrounded, adaperturallyarchingridgesthatextendabouttwo-thirdsofthewayacrossthegrooves
andalternatewithridgesextendingfromtheotherside. Midlineridgezigzaggedintheapicalregion,becoming
straighter adaperturally. Exterior of the test crossed by low, closely spaced transverse wrinkles, barely
perceptiblein theapical regionandincreasingin sizeand spacingadaperturally wrinklesgentlyarchedonthe
;
faces, strongly arched in the corner grooves.
Remarks. Climacoconus quadratus (Walcott), originally described from the Trenton Group (middle
Ordovician) of New York (Walcott 1879), was interpreted by Van Iten (1992a) as having non-
carinate midlines. Comparison of broken type specimens of this species with specimens from the
Elgin Member indicates that this conclusion probably was incorrect.
Climacoconuspumilus (Ladd, 1929)
Plate 2, figures 5-6; Text-figure 3c
1929 Conulariapumila Ladd, p. 384.
1942 Climacoconuspumilus (Ladd); Sinclair, p. 231, pi. 2, fig. 10.
UWBM
Material. 73175-73176 (45 specimens).
Horizon andlocality. Elgin Member, basal Maquoketa phosphorite (Locality 15).
EXPLANATION OF PLATE 2
Fig. 1. Sphenothallus sp.; SUI 84486; upper Ordovician, Maquoketa Formation, Elgin Member, graptolite
shales biofacies; north-eastern Iowa (Locality 1), USA; tubule preserving portions of both longitudinal
thickenings; x 12-2.
Fig. 2. Climacoconousquadratus(Walcott, 1879); SUI84492;upperOrdovician,MaquoketaFormation, Elgin
Member, Lithosome II; south-eastern Minnesota (Locality 17b), USA; inner surface of a minute test
fragment exhibiting part ofa low internal carina at a midline; x40.
Fig. 3. Metaconularia heymani (Foerste, 1920); SUI 62672; upper Ordovician, Maquoketa Formation, Elgin
Member, Unit 3; north-eastern Iowa (Locality 7), USA; plastic cast ofpart ofa single face; the centre of
mm mm
the area shown here lies approximately 10 above the broken apical end (or roughly 20 above the
former apex); x30.
Fig. 4. Climacoconussinclairisp. nov. SUI 84487 upperOrdovician, Maquoketa Formation, Elgin Member,
; ;
Unit 3; north-eastern Iowa (Locality 5), USA; part ofa double row ofI-shaped internal ridges flanking a
midline; x 13-2.
Figs5-6. Climacoconuspumilus(Ladd, 1929);upperOrdovician,MaquoketaFormation, ElginMember,basal
UWBM
Maquoketa phosphoUrWitBe;Mnorth-eastern Iowa (Locality 15), USA. 5, 73175a; relatively large
specimen; x30. 6, 73175b; broken apical end ofspecimen showing the internal carina (arrows) at
the corners; x80.
All are scanning electron micrographs.